Unsaturated polyester resins, which comprise a mixture of an ethylenically unsaturated copolymerizable monomer and a condensation polymer formed by polyesterifying dicarboxylic acids at least a portion of which contains ethylenic unsaturation with dihydric alcohols, can be cured to form thermosetting products which have uses in industry. These resins are particularly useful when glass fibers are dispersed therein as reinforcement. Pipes, panels and the like can be formed from such reinforced thermosetting resins.
In coating applications, curable unsaturated polyester resins are blended with a solvent and with a promoted catalyst system, and then heat cured after the composition is cast as a protective film on a substrate.
The disadvantages of such a coating system are manifold. Unsaturated polyester resins tend to be air-inhibited and do not easily cure into hard tough protective coatings. It is necessary to shield the polyester resin coating from contact with oxygen during the curing cycle. This may require the use of a paraffinic top coat over the polyester resin coating, or the placement of the coated substrate in an inert atmosphere.
The solvent in the conventional polyester coating systems must volatilize during the drying and curing cycle. Even in the case of a polymerizable solvent such as styrene, a considerable quantity of styrene volatilizes under the temperature conditions of the curing cycle.
Furthermore, a high energy input is required to achieve a fully cured thermoset coating. And in many cases, the volatilization of coating composition components is deleterious to the coherency of the coating film.
As a further disadvantage of conventional polyester coating systems, it is necessary to formulate the polyester prepolymer and other polymerizable components of a curable system with the required polymerization catalysts and promoters immediately prior to the spraying or casting of the system. There is a need for polyester coating systems which can be formulated and stored, and then employed directly in coating applications without the inclusion of additional ingredients.
Accordingly, it is an object of this invention to provide curable air-uninhibited unsaturated polyester resin compositions.
It is another object of the present invention to provide polyester coating compositions which do not contain volatile components and which cure as substantially 100% solids systems.
It is another object of the present invention to provide low energy room temperature photocurable unsaturated polyester compositions suitable for coating and molding applications.
It is another object of the present invention to provide unsaturated polyester resin compositions, the curing of which is promoted by the presence of oxygen.
It is a further object of this invention to provide unsaturated polyester resin compositions, the curing of which is promoted by low energy ultraviolet irradiation.
It is still another object of this invention to provide curable polyester resin compositions which are fully integrated polymerization systems which can be preformulated and stored, and then applied as coatings and the like without the need to include additional composition ingredients.
Other objects and advantages of the present invention shall become apparent from the accompanying description and examples.